It is known that once an underwater pipeline is laid on the bed of the body of water, it assumes a configuration imposed by the points or areas that support the underwater pipeline. The laying of an underwater pipeline consequently envisions an accurate preliminary study for a path that avoids the underwater pipeline having spanned portions or spanned portions of excessive length once laid.
EP Patent No. 1,022,501 and PCT Patent Application No. WO 2006/117,249 disclose a technique of laying on a bed of body of water a prefabricated string of a pipeline by variable buoyancy devices, wherein the flexibility of the string enables adaptation to the profile of the bed of the body of water. However, the capability of deformation of the pipeline does not guarantee that the pipeline can follow any profile of the bed.
Sometimes, the preferable path has portions along which ridges and depressions alternate or an escarpment is encountered. In these cases, the morphology of the bed imposes carrying out specific operations to reduce the length of any such spans. A known technique is to carry out operations preparatory to laying the underwater pipeline, such as flattening out the ridges and filling the depressions for example.
In other cases where the bed of the body of water does not have significant discontinuities, it is sufficient to dig a trench in such a way as to create a bathymetric profile for the bottom of the trench as even as possible, as shown in PCT Patent Application NO. WO 2011/061,605 and in the name of the applicant.
Another known technique aimed at rectifying bathymetric profiles characterized by marked variability provides for arranging at least one support in a depression between two successive ridges to provide a further point of support for the underwater pipeline and reduce the length of the free-span portion of the underwater pipeline.
A support of the above-indicated type shown in U.S. Patent Application No. 2014/093317. This support is preliminarily arranged in a given zone of the bed of the body of water and comprises a vertical structure, a carriage selectively movable in a vertical direction along the vertical structure, and a cradle configured to accommodate the underwater pipeline. The underwater pipeline is positioned in the cradle, which is selectively set at a desired height with respect to the bed of the body of water.
A support, based on a similar principle to the previous one is described in U.S. Pat. No. 4,147,455.
PCT Patent Application No. WO 94/08166 shows a straddle carrier, which is laid on the bed straddling the underwater pipeline and is provided with a gripper element capable of grasping a portion of the underwater pipeline and raising this portion until this portion reaches a desired height.
The described supports must be arranged inside a predetermined area and the underwater pipeline must then be coupled to the support.
These operations are relatively costly in terms of time and complicate the laying operations of the underwater pipeline.
All of the described methodologies offer respective advantages and disadvantages and can be conveniently applied depending on the operating conditions encountered in the laying sites, such as depth, morphology, geological structure of the bed of the body of water and the prevailing sea and weather conditions.